An endoscope has been widely used in such fields as the medical field and the industrial field. In general, the endoscope is configured to include an elongated insertion section which is inserted into the body of a subject. A distal end portion of the insertion section is provided with, for example, an illumination optical system for illuminating an examined site and an observation optical system for forming an image of the examined site illuminated by the illumination optical system. If the endoscope is an optical endoscope, a distal end surface of an image guide is disposed at the imaging position of the observation optical system. Meanwhile, if the endoscope is an electronic endoscope, an image pickup device, such as a CCD, is disposed at the imaging position.
The endoscope is classified into a rigid endoscope and a flexible endoscope in accordance with the flexibility of the insertion section. In the flexible endoscope of the two types of endoscopes, the insertion section has flexibility but includes a distal end portion body formed of a rigid material, such as a metal, for example, in the distal end portion of the insertion section. The distal end portion body is fixed with lenses of the above-described optical systems and lens frames for holding the lenses. Further, a distal end portion cover formed of an insulating resin or the like is attached to the distal end portion body from the distal end side so that the distal end portion body formed of a metal or the like is insulated from the outside.
Conventionally, a variety of proposals have been made on a technique of fixing the lenses of the optical systems to the distal end portion body in the above-described configuration.
For example, paragraph numbers [0069] to [0073] of Japanese Unexamined Patent Application Publication No. 2000-135196 describe a technique of fixing a lens to a lens frame by solder bonding and solder-bonding the lens frame to a distal end portion body. A distal end portion cover is then fixed by bonding to the distal end portion body fixed with the lens and the lens frame.
Meanwhile, a paragraph number [0024] of Japanese Unexamined Patent Application Publication No. 2002-85326 describes a technique of fixing a lens by adhering the lens to a distal end portion body and a distal end portion cover. With reference to FIG. 13, description will now be made of the technique described in the Japanese Unexamined Patent Application Publication No. 2002-85326 by taking an example in which the lens forms an illumination optical system. FIG. 13 is a cross-sectional view illustrating a configuration for fixing a cover lens of the illumination optical system in a conventional example. FIG. 13 shows a cross section cut from the central axis O of the insertion direction in such a direction that the cross section includes the illumination optical system.
A distal end portion body 31 is provided with a through hole 31c, and a light guide 45 forming the illumination optical system is disposed in the through hole 31c. On the distal end side of the light guide 45, a cover lens 25, through which illumination light transmitted through the light guide 45 is expanded forward and emitted, is disposed in a distal end surface 21 to be exposed. The cover lens 25 is bonded to the distal end portion body 31 and a distal end portion cover 32 via an adhesive agent 91. The outer circumferential surface of an insertion section is covered by an outer cover tube 41. The outer cover tube 41 is wound around by a wire 42 on the distal end side thereof and fixed by an adhesive layer 43.
In such a configuration as described in the Japanese Unexamined Patent Application Publication No. 2002-85326 and FIG. 13, the cover lens 25 is bonded to the distal end portion body 31 and the distal end portion cover 32 solely by adhesion, as described above. However, an adhered portion exposed outside of the endoscope is often dipped in chemicals such as disinfectant, so that the portion is sometimes eroded by the chemicals. Therefore, though various kinds of adhesives improved to have high resistance against such chemicals are developed, there is a need for joint means which essentially has resistance against chemicals and is capable of ensuring watertightness.
Meanwhile, in such a configuration as described in the Japanese Unexamined Patent Application Publication No. 2000-135196, the lens frame used to fix the lens includes not only the adhered portion but also the soldered portion. Accordingly, the resistance against chemicals can be ensured by the soldered portion. However, in the art disclosed in the publication, the lens frame is required. Therefore, it is inevitable that the diameter of the distal end portion of the endoscope becomes larger than that in a configuration without the lens frame.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an endoscope capable of improving the chemical resistance in the vicinity of an optical member disposed in a distal end portion of the endoscope and enabling a reduction in diameter of the endoscope, a method of manufacturing the endoscope, and an optical member which can be disposed in a distal end portion of an insertion section of the endoscope.